Petroleum related wells, and the like, usually have a tubular string suspended inside a cemented-in casing string that requires special handling during rework, and some other operations. Producing wells often have casing pressures. If the suspended tubular string is pressure sealed to the casing, it behaves as a long piston and the casing pressure can blow the tubular string from the well. To conduct work on such wells a snubbing unit is used. The snubbing unit can secure the tubular string from slipping in either axial direction and can move it in either axial direction. Usually, the snubbing unit is also capable of rotating the string in the well while moving the string in either axial direction.
The bore of the tubular string is closed to the casing pressure before work starts by valves or plugs in the string so that the string can be safely opened during connections.
Before work on the tubular string can begin the casing is sealed from atmosphere by a series of blowout preventers that can each close on and seal a particular size pipe. The greater the number of distinct tubular sizes in the string, the greater the number of blowout preventers required.
The snubbing unit is usually secured to the well head and may be supported solely by the well head or at least partly by a separately prepared structure resting on the earth around the well. The snubbing unit has a base platform fitted with at least one slip bowl and slips to support the string against force in either axial direction. In many cases the stationary slip bowl is a dual bowl arrangement with the dual bowls oppositely oriented with slips to hold in both axial directions. The slips may differ from those usually on rotary rigs in that they can be forced closed without the need for string weight to provide the slip closing force.
The following descriptive material will be directed to adding length to the string, and conducting related activity. Removing string from the well requires alteration of the process but that alteration is well known to those skilled in the art. It will be understood that the same apparatus and basic procedures will work string in either direction as required.
The snubbing unit has a jack mechanism that moves a jack head, situated above the basic platform, axially along the extended well axis. The jack head serves the function of a rig traveling block with the exception that the jack head can push up or pull down on the string. The jack head carries a powered rotary table. The rotary table has a slip bowl with slips that can act in either axial direction or it has two slip bowls, one oriented in each axial direction.
At the present time it is commonplace to move a power tong assembly, usually containing both back-up and lead tongs, into work position around the string and away from the string to clear the work area. In some cases the same power tong assembly is used near the base platform and then hoisted up to operate above the jack head. Around the most dangerous of industrial activity such movements are undesirable.
When practical, hoisting work around a snubbing activity is done with mobile cranes. In some cases, however, the hoist rig comprises a spar mounted on the well head, directly or Indirectly, and fitted with a winch and line for lifting. Such arrangements urge minimization of the lifting and load handling demands.
There is a need to reduce or eliminate human activity on the jack head. An immediate step is to secure the tong set to an adapter plate on the slip bowl. The tong set has to rotate if the slip bowl is rotated. The tong set is never in use while the string is rotated in the well and the tongs can be disconnected from umbelicals and allowed to rotate. Hydraulic and electrical quick couplers remove the challenge from rapid connection and disconnection of the umbelicals to the tong set. That mounting feature is an objective and at least one point of novelty in this invention.
Allowing the tong set to rotate is not a desirable feature in itself but it is expedient with present snubbing unit designs. Further, that overcomes known problems with mounting tongs on the jack head.
An optional feature, an objective and a point of novelty, for the tong arrangement is a mounting structure that permits mounting of the tong set on the jack head structure. The tong set then does not rotate with the slip bowl and the tong umbelicals can remain connected. With that arrangement it is possible to remove the operating personnel from the jack head during routine pipe string working activity. That is a safety feature of substance.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.